Precision optical systems such as interferometers often use beams having precisely controlled positions and directions. However, many types of beam sources deliver beams having positions and/or directions that vary from one beam source to the next. A beam delivered from a remote laser through an optical fiber, for example, has a position and a direction dependent on fiber orientation and collimating lens position. Accordingly, a simple mechanical alignment of the beam source (e.g., the optical fiber) may be unable to provide a beam having a position and a direction within the acceptable tolerances of a precision optical system. Beam manipulators are thus required to precisely shift or deflect the beam from the position and the direction that the source supplies to the position and the direction that the precision optics require.
Beam manipulators often employ reflective surfaces or mirrors that can be adjusted to deflect a beam to the appropriate angle or direction. As a reflective manipulator is adjusted to alter the direction of the beam, there is a factor of two magnification between the adjustment of the manipulator and the angle that the beam moves. This angular magnification and the stability of reflective manipulators is a concern in achieving highest stability in precision optical systems.
Beam manipulators can also use transmissive optics to steer a laser beam in position or direction. FIGS. 1A and 1B illustrate a deflector system 100 using matched wedges 110 and 120, which are sometimes referred to as a Risley prism set, to adjust the direction of a beam 130. Beam 130, which is incident on wedge 110, refracts in accordance with Snell's Law at each of the four air-glass interfaces 111, 112, 121, and 122 of the two wedges 110 and 120.
In the configuration of FIG. 1A, consecutive interfaces 112 and 121 are parallel to each other, and the angular deflection of beam 130 at interface 121 is equal and opposite to the angular deflection of beam 130 at interface 112. Similarly, interfaces 111 and 122 are parallel to each other, and since interfaces 112 and 121 cause no net angular deflection, the angular deflection of beam 130 at interface 122 is equal and opposite to the angular deflection at interface 111. Accordingly, in the configuration of FIG. 1A, system 100 causes no net angular deflection of beam 130.
Wedges 110 and 120 can be rotated with respect to each other to change the relative angle between interfaces 112 and 121. FIG. 1B illustrates a configuration of system 100 where wedge 120 has been rotated so that interfaces 112 and 121 make a maximum angle with each other. In the configuration of FIG. 1B, refractions at interfaces 112, 121, and 122 deflect beam 130 in the same direction, causing the largest angular deflection θmax that system 100 can achieve. Smaller rotations of wedge 120 relative to wedge 110 produce smaller angular deflections, so that system 100 can achieve any desired angular deflection of beam 130 between 0 and θmax. The relative orientations of wedges 110 and 120 can thus be set to provide the desired (polar) angular deflection. System 100 can be also rotated as a unit about its optical axis to adjust an azimuthal angle of the deflection.
Varying a wedge angle (i.e., the angle between surfaces 111 and 112 and between 121 and 122) or the index of refraction of wedges 110 and 120 changes the maximum angular deflection θmax of system 100. The angular range achieved by system 100 is thus a function of the wedge angle and the index of refraction of the glass. A larger wedge angle or refractive index provides system 100 with a greater range for the angular deflections of the beam but makes fine-tuning to the desired angle more difficult. In particular, the angular resolution of system 100 is a function of the wedge angle, the refractive index of the wedges 110 and 120, and the precision achieved for rotations of wedges 110 and 120.
Translators, which control the position of beams, can be similarly implemented using only transmissive optical elements. FIG. 2 illustrates a translator 200 including an optical plate 210 having two plane parallel surfaces 211 and 212. Surfaces 211 and 212 are parallel, so that refraction at surface 211 deflects a beam 230 by an angle that is equal but opposite to the deflection caused by refraction at surface 212. Accordingly, translator 200 preserves the direction of beam 230, but plate 210 translates beam 230 by a displacement D that depends on the thickness L of plate 210, its index of refraction, and the angle that plate 210 makes with incident beam 230. Adjusting the pitch and yaw of plate 210 effectively adjusts the magnitude and direction of displacement D.
A precision optical system using a deflector system 100 as illustrated in FIGS. 1A and 1B or a translator 200, as illustrated in FIG. 2, requires an optical mount that permits precise control of the orientation of the optical elements. Additionally, a change in the temperature of the optical mount should not change the orientations of the optical elements. Preferably, the optical mount would have a low part count to reduce expense and also be compact to permit use in applications having limited space.